Electric translating circuit



D c 15,1942. E. H. B. ATEL|-K 2,305,403

ELECTRIC TRANSLATING CIRCUIT Filed Oct. 13, 1941 60 6.0 FY224 L6) L6! Inventor: Everhard H. BBaPtelink,

b fia/wy C. His Attorney.

Patented Dec. 15, 1942 Search Room ELECTRIC TRAN SLATING CIRCUIT Everhard H. B. Bartelink, Niskayuna, N. Y., assignor to General Electric Company, a corporation of New York Application October 13, 1941, Serial No. 414,720

5 Claims.

My invention relates to wave translating circuits, and more particularly to circuits for transmitting waves having steep wave fronts with minimum distortion.

It is frequently desirable to transmit waves having very steep wave fronts, such as substantially square pulses, from a high impedance circuit to a low impedance circuit without substantial distortion of the waves. It is convenient to utilize for such transmission an electron discharge device having a high input impedance to match the impedance of the circuit from which the wave is to be transmitted, and having an output impedance connected to the cathode of the discharge device and lying in both anode and control electrode circuits. Such an output impedance is of relatively low value, and is suitable for connection in a low impedance output circuit to which the wave is to be transmitted.

In the transmission of waves having very steep wave fronts through such a translating device, interelectrode and various other stray capacities are effective to distort the wave front of the transmitted wave. It is accordingly an object of my invention to provide simplified and improved means for transmitting a wave to a low impedance circuit with minimum distortion.

When substantially square pulses are transmitted through such a translating device, interelectrode and other stray capacities tend to increase the amplitude of the steep wave front of such pulses, and thereby to deform the pulses undesirably. It is a further object of my invention to provide improved and simplified means for compensating for such undesirable increase of amplitude of the wave front of square pulses transmitted through such a device.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner or operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates one embodiment of my invention and Fig. 2 is a series of curves representing certain characteristics thereof.

In Fig. 1 a multivibrator including two electron discharge devices l0 and II generates substantially square pulses, which are transmitted through an electron discharge device l2 acting as a limiter, and through an impedance transforming electron discharge device iii to a low impedance load M.

The multivibrator is of conventional form, and has operating current supply circuits for the devices HI and II which include a source of potential 30, whose negative terminal is grounded. Such circuit for the device In may be traced from the positive terminal of the source 30 through resistances 3i and 21 in series, anode IQ of the device I0, cathode 2|, and a resistance 23 to ground and then back to source 30. The operating current circuit for the device ll extends from the positive terminal of the source 30 through the resistance 3 i, a resistance 28, anode i6 and cathode 22 of device II, and resistance 24 to ground.

The control electrode i! of device I0 is connected through a resistance 25 to ground, and the control electrode 20 of device II is connected through a resistance 26 to ground. The resistances 23 and 24 are proportioned so that the voltage drop therethrough, due to the flow of operating current through the devices [0 and II, produces a suitable bias potential for the control electrodes I1 and 20. To cause the discharge devices IO and II to operate in multivibrator fashion, a condenser I5 is connected from the anode it of device it to the control electrode ll of device l0, and a second condenser I8 is connected from anode IQ of device l0 to control electrode 20 of device ll.

When so connected, 9. small change in potential of any control electrode of either of the devices lil or II initiates operation of the multivibrator. Assume, for example, that the potential of anode l9 rises momentarily. Due to the coupling condenser l8, the potential of control electrode 20 tends also to rise, and more current flows between anode Iii and cathode 22. The potential of anode l6 consequently becomes less positive, and the coupling condenser I5 causes the potential of control electrode I! to become more negative with respect to cathode 2i. This causes current flow through device I0 to decrease, with a resulting additional rise in potential of anode l9. Since a rise in potential of anode l9 initiated the action, such action is cumulative until current flow through device l0 becomes substantially zero, because the potential of control electrode ll becomes more negative than the potential at which current cutoff occurs. Current flow through device II at such time is substantially a maximum.

At that time, when the potentials of the electrodes are substantially constant, such potentials tend to remain at a more or less constant value for a time determined by the resistance and capacity in the multivibrator circuits. After such predetermined time the coupling condensers I5 and I6 no longer maintain constant the potentials of the control electrodes I1 and 26 due to current flow respectively through resistances and 26. Control electrode 26 tends to become more negative, and control electrode I'I tends to become less negative, with the consequence that the entire action of the multivibrator is reversed. A reversed half cycle of operation of the multivibrator thereupon occurs until electrode potentials become substantially constant at the other extreme, for a period of time determined by the resistance and capacity in the multivibrator circuits.

Such action of the multivibrator recurs periodically, and produces substantially square pulses across the resistance 24. To improve the form of these pulses and to make their tops flatter, the electron discharge device I2 is arranged to limit the amplitude of the pulses in the positive direction. (In the negative direction these pulses are limited to a constant value by current cutoff in the device II.) The cathode 32 of the device I2 is connected to the cathode 22 of the device II, and control electrode 33 of the device I2 is connected to ground, so that the square pulses across resistance 24 appear between cathode 32 and control electrode 33. The anode 34 is connected through two resistors 35 and 36 in series to the positive terminal of the source 36, whose negative terminal is grounded. A point between the resistances 35 and 36 is by-passed for high frequency current to ground through a condenser 31. The screen electrode 38 of device I2 is by-passed for high frequency current to ground by a condenser 39, and is maintained at positive potential by a connection through a resistance 46 to a point between resistances 35 and. 36.

Square pulses from the multivibrator appear on the anode 34 of the device I2 with an improved rectangular shape because of the amplitude limiting action of device I2. As may be seen from the explanation of the multivibrator action, the voltage across the resistance 24 recurrently changes at high speed from a low value, substantially zero, to a value such that the cathode 32 is at a substantial positive potential above ground. The resistance 46 is made of high value, so that the screen electrode 38 is at a relatively low positive potential, and current through the discharge device I2 is small relative to the current through the discharge device II. As the voltage across resistance 24 approaches a zero value, current increases through the discharge device I2 and the potential of the anode 34 decreases from a positive value. As such discharge current increases, the anode 34 reaches a substantially constant minimum potential when the potential across the reslstance 24 reaches its minimum, and remains substantially constant because the voltage across resistance 24 is substantially zero.

As the voltage across the resistance 24 increases, so that the cathode 32 becomes positive with respect to ground, a point is reached where current flow through the discharge device I2 is cut off. The multivibrator is arranged a to produce a sufiiciently large voltage change across the resistance 24 to accomplish this current cutoff. During the time when current through device I2 is cut off, the anode voltage 34 remains at a substantially constant value equal to the potential of the source 36, while the voltage of the cathode 22 rises to its maximum positive value, when it may vary to some extent without affecting the potential of anode 34.

The pulses which are reproduced in the .circult of anode 34 of the device I2 are, by reason of the limiting action in the device I2, of a desirably fiat-topped rectangular shape. However, because of the fact that the impedance from the anode 34 to ground is of high value, such rectangular pulses in the circuit of such anode 34 cannot efficiently be impressed directly on a low impedance utilization circuit.

In order to effect an impedance transformation, the discharge device I3 is utilized to transmit such rectangular pulses from the anode circuit of device I2 to the low impedance load I4. A coupling condenser 4| is connected between the anode 34 of the device I2 and the control electrode 42 of the device IS. A resistance 43 is connected between the control electrode 42 and ground, and an output resistance 44, which completes the control circuit of device I3, is connected between ground and the cathode 45 of the device I3. Operating current for the device I3 is supplied to the anode 46 thereof through two resistors 41 and 48, connected in series between the anode 46 and the positive terminal of the source 36. A point between the resistances 41 and 48 is by-passed for high frequency currents to ground through a by-pass condenser 46. The screen electrode 56 of device I3 is by-passed or high frequency current to ground through a condenser 5|, and is supplied with operating current through a resistance 52 connected between screen electrode 56 and a point between resistances 4'! and 48.

The operating current circuit for the device I3 may be traced from the positive terminal of source 36 through resistances 48 and 41, anode 46, cathode 45, and resistance 44 to ground and the negative terminal of source 36. The resist ance 44 produces an operating bias for the control electrode 42 by reason of the discharge current flowing therethrough, and at the same time produces degenerative feedback in the circuits of the device I3, by reason of the fact that it forms a common portion of the control and anodecathode circuits of the device I3.

A low impedance utilization circuit may be energized by the potential across the resistance 44, an eflicient transfer of the rectangular pulses on the anode 34 of device I2 being efiected thereby through the discharge device I3. There are, however, certain capacities in the circuits of the device I3 which produce undesirable effects. Such a capacity, existing between the terminals of the resistance 44, may comprise stray capacities inherent in the resistance 44 itself, as well as capacities between the wires 53 which connect the load I4 in shunt to the resistance 44. Such capacity between the terminals of the resistance 44 is represented by dotted lines 54 on the drawing.

Similarly, capacities exist between the control electrode 42 and the cathode 45, which capacities may include not only interelectrode capacities but also capacity between interconnecting wires and the like. This capacity between the control electrode 42 and the cathode 45 is represented by dotted lines 55 on the drawing. There is similar capacity between the control electrode 42 and the anode 46, which is represented on the drawing by dotted lines 56. This last capacity is minimized by the utilization of the device I3 including screen electrode 50.

It may be seen by inspection that the capacities 54 and 55 form a capacitive voltage divider across the resistance 43, coupling the load l4 thereacross. This capacitive voltage divider, 01. course, acts to transmit high frequencies more easily than low frequencies, because the reactance of the capacities 54 and 55 is so high as to produce negligible coupling, except at high frequencies. The eifect of the coupling from resistance 43 to the load [4 produced by the condensers 54 and 55 is to transmit the steep wave front of rectangular pulses with greater relative amplitude than the lower frequency components of such pulses.

Referring to Fig. 2, curve a represents the potential of the anode 34 with respect to ground, plotted as ordinant, and time, plotted as abscissa. This wave represented by curve a, of course, represents only one particular condition of adjustment of the multivibrator including devices I and II, which may be adjusted to produce pulses of any desired height and width. Curve b of Fig. 2 represents the potential across the resistance 44, as the wave represented by curve a is transmitted through the device I3 without the compensation afforded by my invention. The sharp peak 60 at the beginning of each rectangular pulse, and the oppositely poled sharp clip 6i at the end of each such pulse are caused by action of the capacitive voltage divider including capacities 54 and 55. To illustrate the action of these capacities alone, the curve 0 represents the voltage appearing across the resistance 44 when the cathode 45 is cold and the wave represented by curve a is impressed across resistance 43. Curve 0 shows that a short pulse of voltage appears across the resistance 44 at the leading edge of each of the rectangular pulses of curve a, and an oppositely poled short pulse of voltage appears at the following edge of each rectangular pulse of curve a. It is these pulses of very short duration, which are superimposed on the rectangular pulses transmitted through the device I 3 by electronic action therein, which distort the desired wave form of the rectangular pulses on the resistance 44.

To compensate, or neutralize, these distortions of the desired wave form, a variable condenser 51 is connected between the anode 46 and the cathode 45 of the device l3. The rectangular pulses across resistance 43, which pulses appear on the control electrode 42 of the device i3, appear in inverted form on the anode 46 across the resistance 41. These inverted pulses on the anode 46 are represented by curve d in Fig. 2. Curve d shows no distortion of the rectangular wave form such as in curve 12, because the capacity 56 is so small as to be negligible because of the use of screen electrode 50. Although there is, theoretically a slight rounding of the inverted pulses appearing across resistance 41, such rounding is so slight that it may be disregarded. Because the rounding of pulses on anode 46 is so slight, these pulses on the anode 46 are substantially faithful inversions of the rectangular pulses on the anode 34 of the device i2.

The condenser 51 is adjusted to such a value that the effect of the capacitive voltage divider formed by capacities 54.and 55 on the potential across the resistance 44 is substantially cancelled by the opposite effect of the capacitive voltage divider formed by the capacity 54 and the condenser 51 on the voltage across the resistance 44. By such adjustment of this condenser 51, the peak 60 and dip 6| shown in curve b of Fig. 2 may Search Room be substantially compensated or neutralized, with the result that the voltage across the resistance 44 becomes substantially rectangular as illustrated in curve e of Fig. 2, which is closely similar to curve a.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention,

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in an amplifier for waves having steep wave fronts, of an electron discharge device having an anode, a cathode, and a control electrode, a source of waves having steep wave fronts connected between said control electrode and cathode through a load impedance upon which said waves of steep wave front are reproduced, and means to supply voltage from the anode of said device to said load impedance to neutralize the potential supplied to said load impedance through inherent capacity between said control electrode and cathode.

2. A wave transmission system including a low impedance load, a source of waves having steep wave fronts to be impressed on said load, means to transmit such waves from said source to said load, there being capacity in said means providing coupling between said source and load which tends to transmit undesirable certain components of said waves to said load thereby to distort said wave at said load, means including th anode of an electron discharge device having a control electrode energized by waves from said source for producing waves on said anode similar to said waves on said load and of opposite polarity, and means including a capacity connected between said anode and said load for impressing said oppositely poled waves thereon with such intensity as to reduce said undesired components impressed thereon through said first capacity.

3. In combination, means for transmitting rectangular waves from a source to a load comprising an electron discharge device having an anode, a cathode, and a control electrode, an input circuit between said control electrode and cathode including said source and load, and an output circuit between said anode and cathode including said load, capacity between said source and load being effective to transmit high fre quency components of said wave in greater degree than lower frequency components thereby to distort said waves on said load, means for producing rectangular waves on said anode of opposite polarity to the waves on said load, and means including a capacity between said anode and load for transmitting high frequency components of said rectangular wave on said anode to said load to reduce distortion of the rectangular wave on said load.

4. An electric translating circuit comprising an electron discharge device having an anode, a cathode, and a control electrode, a source of electric pulses having steep wave fronts, a load, an input circuit connected between said control electrode and cathode and including said source and load in series, an output circuit connected between said anode and cathode and including said load, inter-electrode capacity between said control electrode and cathode being effective to exaggerate the steep wave fronts of pulses transmitted by said device from said source to said load, means for causing the potential of said anode to vary oppositely to the potential of said control electrode, and means including capacity between said anode and cathode for transmitting potential variations of said anode to said load in such amount as to reduce the steep wave fronts of pulses on said load to a value like that at said source.

5. A device for transmitting a wave having high frequency components to a low impedance load, said device comprising a source of such a wave, an electron discharge device having an anode, a cathode, and a control electrode, an input circuit between said cathode and control electrode including said source and said load, an

output circuit between said cathode and anode including said load, there being interelectrode capacity between said control electrode and cathode which causes undesired transmission of high frequency components of such wave to said load thereby resulting in distortion of the wave on said lead, means for causing the potential of said anode to vary oppositely to the potential of said control electrode, and means including a capacity between said anode and cathode for impressing the high frequency components of such oppositely varying anode potential on said cathode to reduce said undesired distortion of the wave on said load.

EVERHARD H. B. BARTELINK. 

